A Four-Coordinate Pr Imidophosphorane Complex.

The imidophosphorane ligand, [NPBu] (Bu=tert-butyl), enables isolation of a pseudo-tetrahedral, tetravalent praseodymium complex, [Pr(NPBu)] (1-Pr), which is characterized by a suite of physical characterization methods including single-crystal X-ray diffraction, electron paramagnetic resonance, and L-edge X-ray near-edge spectroscopies. Variable-temperature direct-current magnetic susceptibility data, supported by multiconfigurational quantum chemical calculations, demonstrate that the electronic structure diverges from the isoelectronic Ce analogue, driven by increased crystal field. The four-coordinate environment around Pr in 1-Pr, which is unparalleled in reported extended solid systems, provides a unique opportunity to study the interplay between crystal field splitting and spin-orbit coupling in a molecular tetravalent lanthanide within a pseudo-tetrahedral coordination geometry.